In the engine of an automobile, an exhaust gas recirculation passage for recirculating the exhaust gas thereof to the intake side is provided with the objective of reducing NOx in the exhaust gas or other objectives. An exhaust gas recirculation valve (EGR valve) for opening and closing the passage is provided in the exhaust gas recirculation passage. The EGR valve consists of a valve section and a drive section (actuator section) for the valve section, and a valve shaft in the valve section and a drive shaft in the drive section for driving the valve shaft are formed not integral with each other but separately therefrom for reasons of structure, design, or the like. The opening operation of the valve in the valve section is performed by the abutment and push of the drive shaft in the drive section against and to the valve shaft. The closing operation of the valve is carried out by the urging force of a spring applied to the valve.
In such an EGR valve, when soot (deposit) or the like contained in the engine exhaust gas enters a space between the valve shaft and a bearing thereof and adheres thereto, the valve shaft cannot return to a closed position only by the urging force of the spring and can be fixed in an opened position. Forming the valve shaft integrally with the drive shaft makes it possible to cause the valve shaft to perform opening and closing operations by output of the drive section. Such a technology is disclosed, e.g., in Patent Documents 1, 2, and 3.
Patent Document 1: JP-A-08-151963 (JP-A-1996-151963)
Patent Document 2: JP-A-09-032654 (JP-A-1997-032654)
Patent Document 3: JP-A-08-049785 (JP-A-1996-049785)
However, in the exhaust gas recirculation valve disclosed in Patent Document 1, a valve shaft and a motor shaft is not completely unitized, and further, in the ones disclosed in Patent Documents 2 and 3, the structure for unitizing a valve shaft and a motor shaft is extremely complicated. Furthermore, there is a constraint that the outer diameter of at least one of the shafts cannot be made larger than the outer diameter of a portion sliding in a bearing of the valve shaft (the internal diameter of the bearing).
The present invention has been made to solve the above-described problems, and an object of the present invention is to simplify the structure of an exhaust gas recirculation valve, and further to enable a valve shaft and a drive shaft to be unitized even if a portion of which the outer diameter is larger than the inner diameter of a bearing for supporting the valve shaft is provided on both sides with the bearing as a boundary.